Ubuntu Wired Ethernet Connection Not Working

I recently upgraded my home internet connection to 50 mbps.  Shaw (ISP) gave loaned me a new Cisco DPC3825 cable modem.  The Cisco DPC3825 also functions as a gateway, router, and wireless router, so I pulled the plug on my old Trendnet TEW-432BRP.  In doing this, I started to notice multiple failures between my PS3 and my Ubuntu 11.04 machine (running PS3 Media Server, both wired) in the form of frequent DLNA errors.  On top of this, Ubuntu sometimes wouldn't recognise the wired ethernet connection (even though the hardware lights activated).

Fixing/resetting this was simple:

sudo service network-manager stop
sudo ifconfig eth0 up
sudo dhclient eth0
sudo service network-manager start

These commands stop network manager, ensure the wired ethernet device (eth0 in my case) is being monitored, renew its DHCP lease, and restart network manager.  So far, it's worked for me every time.

After a little more digging, I believe the problem lies with my Cisco SPA2102 VOIP phone adapter.  It was running under the gateway and also assigning DHCP.  I've since turned this feature off and am hoping for less no more communication errors.